PEAVEY CLASSIC 30 HUM whilst playing

[pimpfloyd]

Hi
Just wondering if anyone can help me with a problem I'm having with my peavey classic 30.
Basically I'm getting a low hum underneath the notes.As soon as i stop or deaden the note the hum goes away.It's not very loud but can just be heard underneath whilst i'm playing and it's starting to bug me.This is with the guitar plugged straight into the clean channel with no distortion at low volume.It's more noticeable on single notes with the guitar volume backed off slightly.
I've eliminated everything down to the amp by trying different guitars and leads etc.
I had a close listen around the back of the amp and it seems to be some sort of vibration from the speaker but it's hard to tell as i have to keep playing to make the hum happen.

Anyone heard of this or could offer some advise please?

[Enzo]

Several things come to mind

First is "tube rattle." The EL84 power tubes tend to shake around and some of them rattle inside their glass. Play the guitar to make the sound you describe, then have someone reach into the amp and grasp the power tubes firmly. If that stops the sound you hear, then you have tube rattle and there are things we can do for that. If the tubes are too hot, use a rag or gloves. This is a two-man job.

Next, disconnect the wires from the internal speaker and plug some other speaker into the extension jack. It is possible your original speaker has a rubbing voice coil.

Does it only do this when the volume on clean is over 4 or 5? On that amp the phase inverter startts to clip at about 4 or 5 on the volume control. That adds a little rattiness to the sound. A lower gain tube in V3 socket adds headroom and helps this. I like a 5751 tube there, others use a 12AT7.

[pimpfloyd]

Several things come to mind

First is "tube rattle." The EL84 power tubes tend to shake around and some of them rattle inside their glass. Play the guitar to make the sound you describe, then have someone reach into the amp and grasp the power tubes firmly. If that stops the sound you hear, then you have tube rattle and there are things we can do for that. If the tubes are too hot, use a rag or gloves. This is a two-man job.

Next, disconnect the wires from the internal speaker and plug some other speaker into the extension jack. It is possible your original speaker has a rubbing voice coil.

Does it only do this when the volume on clean is over 4 or 5? On that amp the phase inverter startts to clip at about 4 or 5 on the volume control. That adds a little rattiness to the sound. A lower gain tube in V3 socket adds headroom and helps this. I like a 5751 tube there, others use a 12AT7.

Hi
Sorry for the late reply,my computer's been down for a few days.

I'll try what you mentioned about the tubes and the speaker.
I get the hum with the volume on just 1 or 2(room volume)but I have discovered that it only starts to do it after the amp has been on for 5 or 10 minutes.
Just to clarify,the hum is under every note.As soon as I mute it the hum goes away.

[CharlieP]

You don't mention how old your tubes are. Could it be you have a tube going bad. Has it always done this?

[daz]

If i were a bettin' man, and if i have the chance to bet on this one i just might be, i would say it's one of the maybe 100 or more board jumpers. These are solid core wire jumpers that are what attached the 3 seperate circuit boards together in a C30. had 3 C30's and i have had those things fracture many times, and what can happen is they fracture but the broken ends still make contact, tho obviously a very shaky connection. I have had several symptoms depending on which jumper broke of course. anything from the amp not working at all to what you are describing. if you open the amp up you'll see what i mean by the jumpers. Push each one with the rubber end of a pencil and see if any of them seperate when you do that. These amps are very prone to this if you transport them often. The vibration of the vehicle causes the boards to vibrate and move enough to eventually fracture them. granted, some of those issues i had were likely because the jumpers were weakened by my removing the boards to mod the amp. But i didn't modify all 3, and all 3 at one time or another had this happen to them. Maybe it's just mine, who knows. after all, i have heard of this tube rattle enzo mentioned from a million owners, yet of my 3 C30's not one ever had that issue. So who knows. anyway, this is something else you can look into if it doesn't turn out to be tube rattle or something else.

[pimpfloyd]

Thanks for the info Daz,that sounds pretty complex.The amp is virtually brand new.It has the metal grill at the back to protect the tubes and then the tip of the tube rests on a rubber strip.I presume this is to stop them rattling.

Like I say,it seems to start happening after the amp has been on for maybe 5 or 10 minutes.It makes me think,"ahh it's gone away" and then it starts again.

It's a very low,quiet hum that can just be heard under the note,and it goes with the notes,as soon as i stop playing the hum stops.

Cheers Keith

[12AX7A]

That HUM!

The current production EL84 tubes can't handle the plate voltages found in todays amps. What happens is they become microphonic on a bass note, usually down around G. Hunt for the one note that makes it sound really bad, and if it has gone microphonic there will be one. I find 6 months is about the life for a EL84 that gets regular use. Put in the best repalcement tubes you can find, they will sound better and last longer. No tech needed for this amp and most other EL84 amps, save hi-fi.

You guys that havent experienced these hum issues are no doubt better at keeping fresh tubes in the amp, and letting it cool before moving it.

The issue is actually a ghost note, when ignored it gets worse and turns into hum. Playing the notes down at G simply verify the inevitable.

I am terrible at answering emails, but give it a shot maybe you'll get lucky. Sorry, I sift 800 emails on an average day. If you care to, you can find my toll-free telephone number, just look at my email address and once you visit the site its right there. You can also use my user name, thats my .com too.

Have fun!